2.1 Waterfall background (where is the reader coming from)

It is challenging to use agile methods in the DoD and AF because the workforce has been trained in and has practiced the traditional waterfall methodology for 50+ years. In many ways, the waterfall methodology was implemented as a way to carefully control risk along the development path and accommodate the often stove piped organizations that supported development efforts.
This means that the processes, procedures, acquisition rules, contracting approaches, testing requirements, and so on are all based on the traditional waterfall method.